Ground Loop Isolators?

Just curious what company you guys think makes the best ground loop isolators? I've had engine noise since my first system was installed in my car and I'm on to my 3rd and its still present. I've tried new grounds, checked all connections, etc etc.. I went with the isolators we sell at work but Metra makes awful isolators. It got rid of the noise, but every bump I went over no matter how I had them placed on the amp (hanging freely, taped down to the rack, etc..) my speakers would crack and pop. Take the isolators off and the noise is back but no popping. The isolators themselves just seem rather loose on the connections (I've switched out for new ones, they are all like that) and I think the popping is from the RCA's moving around on the connectors to the amp. I was going to order some Monster Cable ones, but figured I might just be paying for the name.